/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:

    vector<int> ans;

    vector<int> postorderTraversal(TreeNode* root) {


        traversal(root);

        return ans;
    }

    void traversal(TreeNode* root) {

        if (root == nullptr)
            return;

        traversal(root->left);
        traversal(root->right);
        ans.push_back(root->val);

    }
};